The present invention relates to a discharge lamp assembly, in particular, relates to a base structure of the lamp assembly of a discharge lamp for feeding electric power to the lamp. The present invention relates to such a base structure in which a discharge lamp which a base is mounted operates with higher than 20000 volts with no leakage due to undesirable discharge in air and along the base structure itself. The present lamp assembly is preferably used in a head lamp of a vehicle. Preferably, a discharge lamp having the present base structure is compatible with a conventional type socket which is used in a conventional filament type lamp in a head light assembly for a vehicle.
A filament type lamp using tungsten filament has been used for a head light lamp in a vehicle.
Lately, a so-called projector type or ellipsoid head light using a halogen lamp (for instance, an iodine lamp) which has advantages to prevent a lamp wall blackened by halogen cycle and to have long life of a filament has been used in a head light of a vehicle. The lamp is almost a point light source, which is accompanied by a reflector for condensing light.
A technical standard has been determined for such a projector type head light. Some of them are PE (Polyellipsoid), and DE (three-dimentional ellipsoid), in which structure and dimension of a base or a connector are defined for each halogen lamp (H-1 type, or H-7 type, HB-3 type and/or HB-4 type, et al).
A prior halogen lamp for a projector type head light is supplied with electric power of 12 volts, consumes 50-100 watts, having the light conversion efficiency 20-23 lm/W, and average life time 500 hours.
FIG. 8 shows the structure of a prior halogen lamp assembly 100 (H-1 type), and a socket 8 of a projector type head light for accepting said lamp assembly 100.
In the figure, the lamp assembly 100 has a halogen lamp 1, which is fixed to a base 2 through a column 3. The numeral 4 is a flange for fixing the lamp assembly 100 to the socket 8, and 5 is an electrode for feeding electric power to the lamp 1. The halogen lamp 1 operates with low voltage around 12 volts, therefore, no specific consideration for insulation is necessary. The base 2 of the lamp 1 has a column 3 made of plastics, and a flange 4 made of conductive material which doubles as a negative electrode.
A socket assembly 7 has a socket 8 which has a conductive bottom plate 8a. The bottom plate 8a has a hole 9 to which the lamp 1 and the column 3 pass, and a pair of small holes (9a, 9b) for accepting projections 4a on the flange 4 of said lamp assembly 100 so that the lamp assembly 100 is positioned. The lamp assembly 100 is fixed or positioned on the bottom plate 8a, so that the flange 4 contacts with the bottom plate 8a. And a pair of springs 11 push the flange 4 so that the lamp assembly 100 is fixed on the bottom plate 8a. A hook 12 is engaged with the end of the springs 11 so that the lamp assembly 100 is tightly fixed or supported on the bottom plate 8a.
On the other hand, a discharge lamp which replaces a prior halogen lamp is studied for a head light of a vehicle.
A discharge lamp has higher light conversion efficiency up to 100 lm/W, and provides brightness several times as high as a conventional halogen lamp. Further, consumed power is only 35 W or so, and life time is more than four times as long as a halogen lamp. Therefore, a discharge lamp saves much energy, and it is an ideal lamp for a head lamp of a vehicle.
A discharge lamp for a vehicle is commercially available in the tradename XENARC by OSRAM in Germany. Philips Company in Holland also supplies such a discharge lamp in the tradename MICRO POWER LIGHT.
However, as a discharge lamp must use high voltage around 20000 volts, structure for insulation must be considered when it is used as a head light of a vehicle. The structure of a base of a discharge lamp must satisfy the requested specification for insulation.
Conventionally, a base for a discharge lamp for a vehicle is designed in specific size so that spacing between electrodes and length between a positive electrode and an outside ground withstand high voltage higher than 20000 volts.
However, said conventional base structure for a discharge lamp is different in structure and size from those of a conventional filament type head lamp, because of insulation problem for high voltage.
Said conventional base structure for a discharge lamp is comprised of a member of ceramics and a member of metal, or a member of plastics and a member of metal, and has relatively large volume so that leakage and/or discharge due to high voltage, and/or high temperature of a lamp are avoided.
Therefore, it has been impossible to mount a discharge lamp assembly into a conventional socket for a filament type head light. When we use a discharge lamp as a head light for a vehicle, we must develop not only a socket for accepting a discharge lamp, but also a peripheral components which match with the socket.
However, the use of a specific large socket for a discharge lamp, together with peripheral components has the disadvantage of cost for developing some components, and it takes some time for developing, resulting delay of use of a discharge lame as a head light.